Re: Simple explanations. Was: what are the labs for?

["Donald E. Simanek" <dsimanek@eagle.lhup.edu>]

On Sun, 8 Feb 1998, kifer/belk wrote:

> Great brain candy!  I think I understand the slinky, but need to look at
> the rubber band one longer.
>
> I see the slinky as being like the candle in a closed jar or the washers
> on rubber bands hung over the sides of a glass.  When all of these are
> dropped there is zero relative acceleration of gravity for the object in
> free fall.  As that is what makes the candle burn, the washers stay over
> the edge of the cup and the slinky elongate, all of these phenomena
> cease.  How did I do, Don?

The comparison to these other demos seems quite apt. I think that
considering the spring in its own frame of reference could give some
insight.

One thing you might (maybe not) have to deal with in the case of the
spring is that its center of mass is not halfway between its ends, due to
it hanging with each part supporting the weight of everything below. 
Before dropping, the tension is zero at the bottom, and mg at the top, and
the upper coils are stretched apart more than those at the bottom. But
wouldn't it be nice if we could analyze this in detail and find it doesn't
really matter to affect the outcome? 

I'm glad to see this is of interest to some people. I first saw it in one
of Richard Berg's "Physics IQ Test" shows. He didn't attempt to explain it
in the show I attended. Perhaps he thought that his audience (physics
teachers) understood it and didn't need an explanation. He should have
known better, for more than half predicted the wrong result.

	-- Donald

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Dr. Donald E. Simanek                            Office: 717-893-2079
Professor of Physics                                FAX: 717-893-2048
Lock Haven University, Lock Haven, PA. 17745
dsimanek@eagle.lhup.edu                 http://www.lhup.edu/~dsimanek
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